Re: [bcachefs] time of mounting filesystem with high number of dirs aka ageing filesystem

["Marcin Mirosław" <marcin@mejor.pl>]

W dniu 09.09.2016 o 11:00, Kent Overstreet pisze:
> On Fri, Sep 09, 2016 at 09:52:56AM +0200, Marcin Mirosław wrote:
>> I'm using defaults from bcache format, knobs don't have description
>> aboutwneh I should change some options or when I should don't touch it.
>> On this, particular filesystem btree_node_size=128k according to sysfs.
> 
> Yeah, documentation needs work. Next time you format maybe try 256k, I'd like to
> know if that helps.

Hi!

# bcache format --help
bcache format - create a new bcache filesystem on one or more devices
Usage: bcache format [OPTION]... <devices>

Options:
  -b, --block=size
      --btree_node=size       Btree node size, default 256k
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ it's not true

# bcache format  /dev/mapper/system10-bcache
/dev/mapper/system10-bcache contains a bcache filesystem
Proceed anyway? (y,n) y
External UUID:                  1a064a62-fb61-42c8-8f0e-68961ad37d4c
Internal UUID:                  c2802bef-fbc4-414a-9fb0-e071943582c8
Label:
Version:                        6
Block_size:                     512
Btree node size:                128.0K
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


I see another problem, I observed it due to long mount time.
I'm creating many dirs:
# for x in {0..31}; do eatmydata \
mkdir -p /mnt/test/a/${x}/{0..255}/{0..255}; done

# find /mnt/test|wc -l
2105378

df -h shows:
/dev/mapper/system10-bcache          9,8G  421M  9,4G   5% /mnt/test

next I removing all those dirs. Umount, mount:
[ 6172.131784] bcache (dm-12): starting mark and sweep:
[ 6189.113714] bcache (dm-12): mark and sweep done
[ 6189.113979] bcache (dm-12): starting journal replay:
[ 6189.114201] bcache (dm-12): journal replay done, 129 keys in 88
entries, seq 28579
[ 6189.114214] bcache (dm-12): journal replay done
[ 6189.114214] bcache (dm-12): starting fs gc:
[ 6189.118244] bcache (dm-12): fs gc done
[ 6189.118246] bcache (dm-12): starting fsck:
[ 6189.119220] bcache (dm-12): fsck done

So mount time is still long, even with empty fileystem.
df shows:
/dev/mapper/system10-bcache  9,8G  421M  9,4G   5% /mnt/test

# find /mnt/test|wc -l
1

It looks that creating and removing dirs doesn't clean some internal
structures.

Marcin